Field of the Invention
The invention relates to a brush system for an electric motor, having a substantially semi-annular resistor housing with a flat electrical resistor introduced therein, having two resistor terminals which protrude from the resistor housing and can be coupled in an electrically conductive manner with a conductor path of the electric motor, as well as having a substantially semicircular support plate with two bus bars for the electro-conductive coupling of the conductor path to the terminals and having two brush elements, connected to interference-suppression elements, as sliding contacts for a commutator of the electric motor. The invention relates further to an electric motor having such a brush system.
Description of the Background Art
An electric motor, particularly a so-called commutator motor, has a stator and a rotor which is arranged on a motor shaft and is moved within the stator by an alternating magnetic field. The rotor carries a field or excitation winding and the motor shaft has commutator segments, which are fixed to the rotor and brushed by the sliding contact in the form of brushes of a brush system. The brush system and the commutator segments interact during the rotation of the motor axis such that a pole reversal (commutation) of the operating or motor current is achieved. This pole reversal is necessary for the rotational movement of an electric motor operated with a direct current. The brushes typically made as carbon brushes are pressed by spring elements with a spring force against the commutator which is concentric with the motor shaft. During operation of the electric motor, the direct current flows over the brushes and the commutator segments of the commutator into the excitation windings of the rotor.
In this type of electric motor, a stepped speed control occurs in a conventional manner by means of a resistance circuit. The resistance circuit heats up during operation due to the direct current flowing through it. The arising heat generation can lead to overheating of the electric motor, which may have a negative effect on its lifetime.
WO 2005/078907 A1, which corresponds to U.S. Pat. No. 7,511,397, discloses a brush system for an electromotive drive, in which brush system elements with brush elements and interference-suppression elements are fastened to a support plate. Bus bars are provided as conductor tracks for an electrical connection on the support plate. The brush system has a flat resistor disposed in a semicircular resistor housing, whereby the resistor housing has a thermally conductive material and is provided with air passage holes. By integration of the resistor in the brush system and due to the design of the resistor housing with air passage openings, an air-cooled brush system suitable for dissipating or removing heat generated during operation is provided.
In the prior-art brush system, a connecting lug of the flat resistor to a narrow side of the half ring of the resistor housing is provided, as a result of which an effective and space-saving cable routing of the conductor tracks and the positioning of the brush system elements on the base plate are disadvantageously made more complicated. As a result, the production and assembly costs of such brush systems increase disadvantageously.